In computed tomography (CT) imaging systems, an X-ray source emits a fan-shaped beam toward an object, such as piece of baggage at an airport scanner or patient in a medical diagnostic clinic, or any other biological or non-biological object that is being imaged. The X-ray beam is attenuated by the object and subsequently detected by a detector element, such as a Cadmium Zinc Telluride (CdZnTe, or CZT) detector. Other direct conversion detectors such as Cadmium Telluride (CdTe), Gallium Arsenide (GaAs), or Silicon (Si), or any indirect director based on scintillator material may also be used in CT imaging systems. Image slices collected by scanning the object may, when joined together, produce 3-dimensional cross-section images of the object.
In typical CT imaging systems, a detector array that includes a number of detector elements may each produce a dedicated electrical signal that indicates the level of attenuation received by each detector element. The electrical signals may be transmitted to a data processing card for analysis. Finally, using image reconstruction techniques an image is produced. The intensity of the attenuated beam received by each detector element is dependent upon the attenuation of the X-ray beam by the object. For example, when scanning a human body, bone turns up white, air turns up black, and tissues and mucous turn up in shades of gray. When no object is present in the CT scanner the detected intensity, or count rate, could reach values as high as 109 counts per second per millimeter squared (cps/mm2). On the other hand, if the scanned object is thick the count rate could be orders of magnitude lower. Thus the detected count rate could vary significantly during the X-ray tube rotation process while the image is being acquired.